The present invention relates to an apparatus and method for detecting occupancy of a channel within a frequency band, and in particular to a frequency-selective occupancy measurement based on a threshold determined from the noise floor.
In order to be able to perform frequency-selective spectrum occupancy measurement of radio channels, for example, exact determination of a threshold is necessitated, above the value of which the channel to be measured is classified as currently active, or below which the channel is classified as currently inactive.
Further, by frequency-selective spectrum occupancy measurement of radio channels, it can also be determined which radio channels are occupied to what extent over time and whether the channel parameters, such as center frequency or maximum field strength are maintained.
The threshold can, for example, simply be firmly set to a power level value measured, for example, in dBm, for the period of the measurement. The disadvantage of this method is that the receive spectrum (power spectral density=PSD) changes significantly in parts when the receiver (e.g. the antenna, bandwidth, etc.) changes. Thereby, it can become necessitated to readjust the threshold every time.
It is also possible to determine the threshold adaptively from the current receive spectrum, for example by determining the noise floor and adding an offset in decibel (dB) to the same, so that the so-called noise riding threshold (NRT) is obtained. However, it is a disadvantage of this method that in real situations, due to the structure of the receiver, receive spectra are to be measured which are not flat but, for example, arranged in a rising manner towards higher frequencies or also in a falling manner. In this case, the radio channels are classified as active or inactive, depending on their position in the receive spectrum, which results in measurement errors.
It follows that there is a need for an apparatus and a method allowing the occupancy measurement of a radio channel to be performed frequency-selectively, flexibly and largely independent from the hardware.